In recent years, a ladder filter formed by combining elastic wave resonators, each of which has a terminal pair, has been widely used at an RF stage of portable phones. A longitudinally coupled resonator type elastic filter including plural electrode pairs has been also widely used in the RF stage.
FIG. 11 shows an electrode pattern of conventional elastic wave device 501. Elastic eave device 501 includes piezoelectric substrate 1, a pair of reflecting electrodes 2 and a pair of comb-shaped electrodes 5. Both of electrodes 2 and 5 are formed on substrate 1. Comb-shaped electrode pair 5 is disposed between the pair of reflecting electrodes 2, and electrode pair 5 interdigitates. Comb-shaped electrode 5 includes common electrode 3 and plural electrode fingers 4 connected to common electrode 3. Elastic wave device 501 constitutes an acoustic surface wave resonator on piezoelectric substrate 1 for trapping energy of the elastic wave therein.
In recent years communication devices have been downsized and the frequency band to be used has been densified due to a large number of users, so that a highly efficient elastic wave device having less insertion loss is required for those communication devices to operate reliably.
A conventional elastic wave device similar to elastic wave device 501 is disclosed in Patent Literature 1.